This invention relates to photocathodes made of semiconductor single crystals, and more particularly to the photoelectric surface of the photocathode.
A photocathode made of a single crystal of a semiconductor such as gallium arsenide has very high sensitivity. In a conventional method of manufacturing a photoelectric cathode of this type, its photoelectric surface is mechanically abraded and uneven or rough parts of the photoelectric surface thus treated are removed, or smoothed, by a chemical etching method, so that the photoelectric surface is smooth like a mirror.
In the case where a light beam is detected by means of a photoelectric tube or a photomultiplier, the light beam is ordinarily applied to it through an optical system comprising a spectroscope, a reflective mirror, etc. In this case, the incident light beam is often polarized because it is reflected and refracted by the optical system. When this polarized light beam is applied to the mirror-like photoelectric surface of the conventional photocathode described above, its apparent sensitivity depends on the angle formed by the incident surface with the electric field vector of the polarized light beam. Accordingly, even if the intensity of the incident beam is kept unchanged, the photoelectric output of the photocathode depends on the conditions of arrangement of the optical system, which causes errors in the measurement of the light beam.